Circulation of drilling fluids during the drilling of subterranean wells is necessary for the operation of numerous down hole tools, such as turbines and delicate measurement instruments. It is desirable that the drilling fluid does not contain particles of a size that will damage the tool and necessitate pulling the drill string and repairing or replacing the tool. In an attempt to avoid this problem drilling fluids are filtered to remove the damaging particles before being re-circulated down hole. These methods and devices work well for removing particles before the fluid enters the drill string, however it is well known that damaging scale particles often originate from locations within the drill string where scale or cement builds up and eventually is knocked loss and carried along with the drilling fluid stream into contact with valuable and delicate down hole tools. Scale on the interior surface of the drill string originate from numerous sources such as rust, ferrous carbonate, and iron sulfide deposits. While cement is deposited on the interior of the drill string during cementing operations. Scale and cement deposits are known to be freed from the tubular walls by the forces created by drilling operations, moving the drill string, or the flow of drilling fluid. The loose cement or scale particles are a constant source of blockage and/or damage of down hole tools. When the tool is damaged or plugged by these particles the entire drill string must be tripped out of the hole in order to remove the occlusion or repair the tool resulting in valuable rig down time. Presently, the recommended practice to prevent these problems include time consuming procedures such as the following:
1. Rabbit all pipe and subsequent pipe joints. PA1 2. High pressure cleaning of the pipe interior using a pig. PA1 3. Knock loose debris off the interior walls of drilling pipe with a hammer. PA1 4. Wash the interior of the pipe with available rig water. PA1 5. Circulate drilling fluid for an additional period of time at full stroke during fill-ups at trips to prevent the particles from settling and blocking tools. PA1 6. Run a caustic sweep prior to retrieving tools.
A filtering option is disclosed by Beimgraben U.S. Pat. No. 4,495,073 which describes a filtering device or screen incorporated within any location of a drill string and which is retrievable by fishing tools. This device is useful for filtering fluids in close proximity to down hole tools, however when the clogged filter screen is withdrawn from deep in the drill string, scale is frequently dislodged from the interior surface and collar joints of the drill string and allowed to fall down hole behind the filter and ultimately into contact with down hole tools. Additionally, the filter screen has relatively low capacity and is frequently clogged resulting in undesirable down time.
The present invention provides an alternative to the present practices employed to remove scale and/or cement described above and overcomes problems with filtering drilling fluid by providing a filtering device that removes damaging particles from the fluid by facilitating the erosion of damaging particles in the drilling fluid stream to a size that can easily pass through down hole tools without damage. The present device is retrievable by wire line, may be placed at any location in the drill string, includes wipers that assist with the removal of scale or cement from the interior surface of the drill string when the filter is retrieved, may be placed in close proximity to down hole tools, is rarely clogged by scale or cement particles, is easily cleaned, may be used with electronic wire routed through the device, and is easily reinserted into place with minimal down time.
The present invention also provides a means for breaking up plugs of lost circulation material (LCM). LCM consist primarily of wood particles, nutshells, paper, cellophane, sugar cane pulp, cotton seed hulls, acid soluble cement or minerals and are graded as either fine, medium or course particle size. LCM is known to form plugs or clumps which, when pumped down hole plug tools and down hole screens. Pulser screens with slots are used to break up medium or course LCM while a pulser screen with round openings is used to break up fine graded LCM. Prior to the present invention running both fine-medium or fine-course LCM would virtually assure a tool failure. The present invention breaks up clumps of LCM composed of any grade with out the need for pipe screens thus allowing for the addition of any grades of LCM to the drilling fluid.